Lubricating Oil Additives

ABSTRACT

A lubricating oil composition comprising at least 50 percent by mass, based on the mass of the composition of an oil of lubricating viscosity and 0.01 to 25 percent by mass, based on the mass of the composition of a polymer comprising units (a) and one or both units (b) and (c): 
       —N(COR 1 )(CH 2 ) x —  (a)
 
       —NH(CH 2 ) y —  (b)
 
       —N(CH 2 CH 2-k (CH 3 ) k COOR 2 )(CH 2 ) z    (c)
         where the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1. The polymer shows good solubility in the lubricating oil and provides friction modification. A method of synthesising a polymer is also disclosed.

FIELD OF THE INVENTION

This invention relates to lubricating oil compositions containingpolymeric additives useful for example, to lubricate the crankcase ofspark-ignited or compression-ignited internal combustion engines. Moreespecially, the additives provide friction modifying properties tolubricating oils and are polymers containing units which are derivedfrom oxazoline monomers or oxazine monomers. The polymers also have goodsolubility in base oils and do not have an adverse effect on lubricantviscosity.

BACKGROUND OF THE INVENTION

There is much interest in improving the fuel economy of gasoline anddiesel engines. This can be done, through the lubricant engine oil, byreducing the friction contribution either of the bulk fluid (by loweringthe oil viscosity) or improving the friction of the contacting parts byinclusion of friction modifier additives.

There is therefore interest in additives with low friction properties inlow viscosity oils.

It is also important that additives used in lubricating oils have goodsolubility, in order for the oils to remain stable under prolongedstorage.

Dispersant viscosity modifier (DVM) additives are known to providefriction modification Examples known in the art, based on polymertechnology, are olefin copolymers (OCP) and methacrylate copolymers. Aproblem with such additives especially in applications which requireultra-low viscosity lubricating fluids such as 0W-8, 0W-16, 0W-20 istheir high thickening efficiencies.

Poly(2-oxazoline)s are known in the art. For example, the art describesthe living cationic ring-opening polymerization of 2-oxazolines. SeeHoogenboom et al., Angew. Chem. Int. Ed 2009, 48, 7978-7994. U.S. Pat.No. 4,120,804 describes the use of short oligomers of poly(2-oxazoline)shaving 2 to 15 repeating units as dispersants to prevent or reduce theformation of sludges, or to neutralise acidic components etc. inlubricating oils. The polymerisation initiator is a polymeric materialof molecular weight equal to or greater than 250 and the oxazoline is2-substituted with a hydrocarbyl group of 1-18 carbon atoms. No mentionis made of friction modification, or of lubricant viscosity impact.

Polyoxazines are also known in the art see Hoogenboom et al., Macromol.,2011, 3420. U.S. Pat. No. 4,001,147 describes certain polyoxazines asuseful to remove phenolic compounds from aqueous waste streams.

U.S. Pat. No. 5,439,978 describes the use of both oxazoline andoxazine-based copolymers as additives to render electrically conductive,nonconductive materials such as plastics.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a lubricating oil compositioncomprising at least 50 percent by mass, based on the mass of thecomposition of an oil of lubricating viscosity and 0.01 to 25 percent bymass, based on the mass of the composition of a polymer comprising units(a) and one or both units (b) and (c):

—N(COR¹)(CH₂)_(x)—  (a)

—NH(CH₂)_(y)—  (b)

—N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c)

wherein the total number (n) of units (a), (b) and (c) is an integerbetween 4 and 500; wherein x, y and z are independently 2 or 3; whereink is zero or 1;

wherein the polymer carries an inorganic or organic nucleophilicpolymerisation terminating group (t), and an initiator group (i)connected to the N atom of a unit (a), (b) or (c), the initiator group(1) being effective to initiate the polymerisation of linear, branchedor cyclic hydrocarbyl moieties;

wherein R¹ comprises a single or a mixture of linear, branched or cyclichydrocarbyl groups having 1-50 carbon atoms, some or all having 12-50carbon atoms, or of at least one macro-monomeric hydrocarbyl group withmore than 50 carbon atoms; and

wherein R² comprises a substituted or unsubstituted hydrocarbyl grouphaving 1 to 30 carbon atoms, which group may be, linear or branched orcyclic, saturated or unsaturated, or aromatic.

In preferred embodiments, group R² is a substituted hydrocarbyl groupwhich may carry one or more hetero atoms, functional groups or has beenmodified by reaction with other moieties. This enables the polymer to beprovided with chemical and/or physical properties which may provideadditional benefits when used in lubricating oil compositions. Somenon-limiting examples of suitable groups R² will be apparent from thedescriptions hereinbelow.

In a second aspect, the invention provides a method of lubricating thecrankcase of an internal combustion engine comprising operating theengine and lubricating the crankcase with a lubricating composition ofthe first aspect of the invention in the faun of a crankcase lubricant.

In a third aspect, the invention provides the use of a polymercomprising units (a) and one or both units (b) and (c):

—N(COR¹)(CH₂)_(x)—  (a)

—NH(CH₂)_(y)—  (b)

—N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c)

wherein the total number (n) of units (a), (b) and (c) is an integerbetween 4 and 500; wherein x, y and z are independently 2 or 3; whereink is zero or 1;

wherein the polymer carries an inorganic or organic nucleophilicpolymerisation terminating group (t), and an initiator group (i)connected to the N atom of a unit (a), (b) or (c), the initiator group(i) being effective to initiate the polymerisation of linear, branchedor cyclic hydrocarbyl moieties;

-   -   wherein R¹ comprises a single or a mixture of linear, branched        or cyclic hydrocarbyl groups having 1-50 carbon atoms, some or        all having 12-50 carbon atoms, or of at least one        macro-monomeric hydrocarbyl group with more than 50 carbon        atoms; and

wherein R² comprises a substituted or unsubstituted hydrocarbyl grouphaving 1 to 30 carbon atoms, which group may be, linear or branched orcyclic, saturated or unsaturated, or aromatic, in a lubricating oilcomposition for an internal combustion engine to provide the lubricatingoil composition, in operation of the engine, with friction reducingproperties.

As described in EP 3257921 A1 and co-pending applications EP 18199179.5,EP 18203212.8 and EP 18199804.8, units (a), (b) and (c) of the polymermay be derived from 2-substituted-2-oxazoline monomers, in the casewhere x, y or z are equal to 2, or from 2-substituted-2-oxazinemonomers, in the case where x, y or z are equal to 3. When mixtures of2-substituted-2-oxazoline monomers and 2-substituted-2-oxazine monomersare used, the values for x, y and z will be 2 in some cases and 3 inothers

As described in more detail hereinbelow, the polymer may be prepared byfirst polymerising one or more 2-substituted-2-oxazoline monomers, oneor more 2-substituted-2-oxazine monomers, or a mixture of one or more2-substituted-2-oxazoline monomers and one or more2-substituted-2-oxazine monomers, for example by living cationicring-opening polymerization, to form a polymer comprising only units(a). Subsequent partial hydrolysis can then be used to convert someunits (a) into units (b). Units (b) can then be converted by reactionwith an acrylate or methacrylate species to introduce units (c) into thepolymer, which may be further reacted to introduce additionalfunctionality. Several embodiments are possible, for example the step toconvert units (b) into units (c) may be omitted such that the polymercomprises units (a) and (b) but not (c). Alternatively, some units (b)may be converted into units (c) such that the polymer comprises units(a), (b) and (c). Further alternatively, all units (b) may be convertedinto units (c) such that the polymer comprises units (a) and (c) but not(b).

The relative proportions of units (a), (b) and (c) in the polymer may beany suitable values and will be determined by both the extent ofhydrolysis and the subsequent extent of further reaction to produceunits (c), if present. In embodiments where units (c) are not present,the polymer may contain up to 60 mol %, preferably up to 50, 40, 30 25,20 or 10 mol % of units (b). Similarly, where units (b) are not present,the polymer may contain up to 60 mol %, preferably up to 50, 40, 30 25,20 or 10 mol % of units (c). In embodiments where units (a), (b) and (c)are present, the polymer may contain up to 60 mol %, preferably up to50, 40, 30 25, 20 or 10 mol % of units (b) and (c) combined, where themolar ratio of units (b): units (c) ranges from 1:10 to 10:1, preferablyfrom 1:5 to 5:1, for example 1:2 to 2:1.

DETAILED DESCRIPTION OF THE INVENTION Definitions

In this specification, the following words and expressions, if and whenused, have the meaning given below:

“active ingredients” or “(a.i.)” refers to additive material that is notdiluent or solvent;

“comprising” or any cognate word specifies the presence of statedfeatures, steps, or integers or components, but does not preclude thepresence or addition of one or more other features, steps, integers,components or groups thereof. The expressions “consists of” or “consistsessentially of” or cognates may be embraced within “comprises” or anycognate word. The expression “consists essentially of” permits inclusionof substances not materially affecting the characteristics of thecomposition to which it applies. The expression “consists of” orcognates means only the stated features, steps, integers components orgroups thereof are present to which the expression refers;

“hydrocarbyl” means a chemical group of a compound that containshydrogen and carbon atoms and that is bonded to the remainder of thecompound directly via a carbon atom. The use of the qualifier“substituted” means that the hydrocarbyl group may contain one or moreatoms other than carbon and hydrogen (“hetero atoms”). Those skilled inthe art will be aware of suitable groups (e.g., halo, especially chloroand fluoro, amino, allcoxyl, carboxy, ester, mercapto, alkylmercapto,nitro, nitroso, sulfoxy, etc.). The group may be unsaturated, and/or maybe polymeric;

“oil-soluble” or “oil-dispersible”, or cognate terms, used herein do notnecessarily indicate that the compounds or additives are soluble,dissolvable, miscible, or are capable of being suspended in the oil inall proportions. These do mean, however, that they are, for example,soluble or stably dispersible in oil to an extent sufficient to exerttheir intended effect in the environment in which the oil is employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of higher levels of a particular additive, ifdesired;

-   -   “ashless” in relation to an additive means the additive does not        include a metal;    -   “ash-containing” in relation to an additive means the additive        includes a metal;    -   “major amount” means in excess of 50 mass % of a composition or        mixture;    -   “minor amount” means 50 mass % or less of a composition or        mixture;    -   “effective amount” in respect of an additive means an amount of        such an additive in the composition (e.g. an additive        concentrate) that is effective to provide, and provides, the        desired technical effect;    -   “ppm” means parts per million by mass, based on the total mass        of the composition;    -   “metal content” of a composition or of an additive component,        for example molybdenum content or total metal content of the        additive concentrate (i.e. the sum of all individual metal        contents), is measured by ASTM D5185;    -   “TBN” in relation to an additive component or of a composition,        means total base number (mg KOH/g) as measured by ASTM 1J2896;    -   “KV₁₀₀” means kinematic viscosity at 100° C. as measured by ASTM        D445; HTHS means High Temperature High Shear at 150° C. as        measured by—CEC-L-36-A-90.    -   “phosphorus content” is measured by ASTM D5185;    -   “sulfur content” is measured by ASTM D2622;    -   “sulfated ash content” is measured by ASTM D874;    -   M_(n) means number average molecular weight as measured by Gel        Permeation Chromatography with reference to linear narrow        poly(methylmethacrylate) standards in the range of 550 to        600,000 g/mol;    -   M_(w) means weight average molecular weight as measured by Gel        Permeation Chromatography with reference to linear narrow        poly(methylmethacrylate) standards in the range of 550 to        600,000 g/mol;    -   “dispersity” means M_(w)/M_(n), (denoted by Ð)

Also, it will be understood that various components used, essential aswell as optimal and customary, may react under condition of formulation,storage and use and that the invention also provides the product(s)obtainable or obtained by any such reaction.

Further it is understood that any upper and lower quality, range orratio limits set forth herein may be independently combined.

Polymers

As discussed above, the polymers useful in the present invention may bemade in a stepwise manner.

In a first step, a polymer is formed having only units (a). This polymermay be a homopolymer or a copolymer. A homopolymer may be formed bypolymerising one or more 2-substituted-2-oxazoline monomers or one ormore 2-substituted-2-oxazine monomers. It will be understood that ahomopolymer in this context means that only one type or class of monomeris used, i.e. either an oxazoline or an oxazine, and not necessarilythat each monomer used is identical (c.f. polyethylene as an example).Polymers which are obtained from a mixture of the same type or class ofmonomer, for example two or more different 2-substituted-2-oxazolinemonomers or two or more different 2-substituted-2-oxazine monomers, areintended to be captured under the description of homopolymer.

Copolymers having only units (a) may be formed by polymerising one ormore 2-substituted-2-oxazoline monomers and one or more2-substituted-2-oxazine monomers. In this case, as is known in the art,the copolymers may be of different types. As examples of copolymersthere may be mentioned statistical copolymers which are formed where thepolymerisation follows a known statistical rule, for exampleBernouillian statistics or Markovian statistics. A statistical copolymerwhere the probability of finding a particular type of monomer residue atany particular point in the polymer chain is independent of the types ofsurrounding monomers can be referred to as a random copolymer.Statistical and random copolymers may be distinguished from more orderedcopolymer types such as alternating copolymers, periodic copolymers andblock copolymers. Block copolymers, i.e. in which two or more polymersub-units are linked by covalent bonds (e.g. as di- or tri-blocks) maybe used. The blocks in any block copolymer may be of equal size or ofdifferent sizes and the architecture of the copolymers can vary. Forexample, block copolymers may have only a single block of each monomer(i.e. in a ‘AB’ arrangement) or multiple blocks of each monomer (i.e. inan ‘ABABAB..’ arrangement) where blocks ‘A’ and ‘B’ may be the same sizeor of different sizes

Also noteworthy are branched copolymers, in particular star polymerswhere several (three or more) linear polymer chains (or “arms”) arecovalently bonded to a central core.

The polymer (or copolymer) having only units (a) is conveniently formedby polymerising 2-substituted-2-oxazoline monomers and/or2-substituted-2-oxazine monomers with an initiator and subsequentlyterminating polymerisation. Any cationic species is capable ofinitiating polymerization of 2-oxazolines or 2-oxazines. Examplesinclude H⁺ (from HCl or other acids); R⁺ (for example from alkyl halidessuch as RI or RBr); and metal cations and salts (e.g. Zr⁴⁺). Anynucleophilic species is capable of terminating the polymerization (e.g.OH⁻ from atmospheric water, OTs⁻(tosylate), H₂NR, HSR). Other suitableinitiator groups (i) and terminating groups (t) will be known to thoseskilled in the art. Multifunctional initiators or terminators, crosslinking or coupling can be employed to provide star architectures.

In a second step, the polymer having only units (a) is partiallyhydrolysed to convert some units (a) into units (b). Hydrolysis of suchpolymers is facile and suitable techniques and methods will be known tothose skilled in the art. One preferred method is to treat the polymerwith a mixture of aqueous hydrochloric acid and THF but other optionswould include reaction under basic conditions using aqueous sodiumhydroxide or methanolic sodium hydroxide in mixture with a suitablesolvent. It is important in the context of the present invention thatnot all units (a) are converted to repeat units (b), that is, fullhydrolysis should be avoided. As discussed above, any degree of partialhydrolysis is possible however in embodiments, hydrolysis yields apolymer containing up to 60 mol %, preferably up to 50, 40, 30 25, 20 or10 mol % of units (b).

In one embodiment, the polymer obtained from the second step is notreacted any further. Preferably however, in another embodiment, thepolymer is further reacted in a third step to convert some or all of theunits (b) into units (c), Preferably in this third step, a Michaeladdition reaction is performed whereby the polymer from the second stepis reacted with an acrylate or methacrylate species. Any acrylate ormethacrylate species may be used however a species which facilitatesfurther reaction or functionalisation is preferred. Acrylates arepreferred over methacrylates. It will be understood that in thestructure given for units (c), when an acrylate is used, the value k iszero and when a methacrylate is used, k is equal to 1. A preferredspecies is propargyl acrylate (prop-2-yn-1-yl-acrylate).

In the preferred embodiment where the polymer comprises units (c),preferably R² comprises an alkynyl group of the structure —(CH₂)_(m)CCH,where m is an integer from 1 to 10. Preferably m is 1 such that R² isprop-1-ynyl. In this case, units (c) will have a structure (I):

Further examples are analogous structures (I) where R² is an alk-1-ynylgroup with more carbon atoms than prop-1-ynyl, i.e., m>1.

The terminal alkynyl group in structure (I) above permits furtherreaction to produce units (c) where R² is a substituted hydrocarbylgroup.

In a preferred embodiment, R² comprises a hydrocarbyl group terminallysubstituted by a 1,2,3-triazole group. Preferably, the 1,2,3-triazolegroup is substituted with a hydrocarbyl group having 1 to 50 carbonatoms, preferably 1 to 30 carbon atoms. Preferably, polymers comprisingunits (c) which have structure (I) are further reacted with an azide,for example an alkyl azide. An azide-alkyne “click” reaction can be usedto produce units (c) having structure (II):

where R³ is preferably a hydrocarbyl group or a substituted hydrocarbylgroup having 1 to 50 carbon atoms, more preferably a hydrocarbyl groupor a substituted hydrocarbyl group having 1 to 30 carbon atoms.Preferably, R³ is a substituted hydrocarbyl group.

In another preferred embodiment, R² comprises a hydrocarbyl groupterminally substituted by one or more thioether groups. Preferably,polymers comprising units (c) which have structure (I) are furtherreacted with a thiol, for example a primary alkylthiol. A thiol-yne“click” reaction can be used to produce units (c) having structures(III):

where preferably R⁴ and R⁵ are independently hydrocarbyl groups orsubstituted hydrocarbyl groups having 1 to 50 carbon atoms, morepreferably hydrocarbyl groups or substituted hydrocarbyl groups having 1to 30 carbon atoms. Preferably R⁴ and R⁵ are independently substitutedhydrocarbyl groups.

Preferably, the total number (n) of units (a), (b) and (c) in thepolymer is from 10 to 300, preferably 25 to 300, more preferably 25 to100.

Preferably, the polymer has a number average molecular weight (Mn) of2,000-500,000 g/mol. More preferably, the polymer has a number averagemolecular weight (Mn) of 4,000-100,000 g/moL Even more preferably, thepolymer has a number average molecular weight (Mn) of 6,000-50,000g/mol, for example 8,000-20,000 g/mol. All molecular weights are asmeasured by Gel Permeation Chromatography with reference to linearnarrow poly(methylmethacrylate) standards in the range of 550 to 600,000g/mol.

In an embodiment, the copolymer has a star architecture with three ormore arms, and a number average molecular weight (Mn) of 10,000-500,000g/mol, R¹ and/or R² having at least some groups of 12-50 carbon atoms inat least one arm. All molecular weights are as measured by GelPermeation Chromatography with reference to linear narrowpoly(methylmethacrylate) standards in the range of 550 to 600,000 g/mol.

When R¹ is a macro-monomeric hydrocarbyl group, it may be provided via

-   -   a) polymerization from a reactive group in an R¹ precursor; or    -   b) incorporation of a pre-formed macro-monomeric in hydrocarbyl        group in an R¹ precursor.

The significance of the presence of R¹ groups having 12-50 carbon atomsis to make the copolymers sufficiently oleophilic to confer solubilityin a polar media such as base oil.

Preferably R¹ contains 1 to 36, more preferably 1 to 20 carbon atoms,provided that some or all of the groups R¹ have 12 to 75, preferably 12to 50, for example 12 to 36 carbon atoms.

As examples of the number of carbon atoms in W, there may be mentioned1, 2, 8, 12, 17 and 24.

In a preferred embodiment R¹ comprises unsaturated hydrocarbyl groupshaving between 8 and 20 carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymercomprise unsaturated hydrocarbyl groups having between 8 and 20 carbonatoms. More preferably, at least 10%, or 20% or 30% or 40% or 50% of thetotal number of groups R¹ in the polymer comprise unsaturatedhydrocarbyl groups having between 8 and 20 carbon atoms. Mostpreferably, at least 60% or 70% of the total number of groups R¹ in thepolymer comprise unsaturated hydrocarbyl groups having between 8 and 20carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymercomprise unsaturated hydrocarbyl groups having between 15 and 20 carbonatoms. More preferably, at least 10%, or 20% or 30% or 40% or 50% of thetotal number of either or groups R¹ in the polymer comprise unsaturatedhydrocarbyl groups having between 15 and 20 carbon atoms. Mostpreferably, at least 60% or 70% of the total number of groups R¹ in thepolymer comprise unsaturated hydrocarbyl groups having between 15 and 20carbon atoms.

Preferably, at least 5% of the total number of groups R¹ in the polymercomprise unsaturated hydrocarbyl groups having 17 carbon atoms. Morepreferably, at least 10%, or 20% or 30% or 40% or 50% or 60% of thetotal number of groups R¹ in the polymer comprise unsaturatedhydrocarbyl groups having 17 carbon atoms. Even more preferably, atleast 70% of the total number of groups R¹ in the polymer compriseunsaturated hydrocarbyl groups having 17 carbon atoms.

In an embodiment, groups R¹ do not contain any hetero-atoms, i.e. arehydrocarbon groups. Preferably groups R¹ are hydrocarbon groups.

In preferred embodiments, at least 50% of the total number of groups R¹in the polymer comprise singly, doubly or triply-unsaturated C₁₇ alkenylgroups or any mixture thereof. More preferably, at least 60% of thetotal number of groups R¹ in the polymer comprise singly, doubly ortriply-unsaturated C₁₇ alkenyl groups or any mixture thereof. Even morepreferably, at least 70% of the total number of groups R¹ in the polymercomprise singly, doubly or triply-unsaturated C₁₇ alkenyl groups or anymixture thereof.

In particularly preferred embodiments, groups R¹ comprise a mixture ofsingly, doubly or triply-unsaturated C₁₇ alkenyl groups which mixturepredominates in singly, and doubly-unsaturated C₁₇ alkenyl groups. Suchmixtures may comprise small amounts of smaller and longer molecules.

Suitable sources for mixtures of groups for R¹ include 2-oxazolines and2-oxazines derived from natural fatty acids such as tall oil fatty acid(TOFA) and rape-seed oil fatty acid. Other suitable sources will beknown to those skilled in the art.

In an embodiment, R¹ may contain hetero atoms (such as N, O, S, P, B,Si, F, Cl, Br, I). As discussed hereinabove, the term ‘hydrocarbyl’ whenapplied to R¹ (and R²) permits the presence of a limited number ofhetero atoms and so is not limited to groups which contain carbon andhydrogen only.

The synthesis of the polymer forms another aspect of the presentinvention and so in a fourth aspect, there is provided a method forsynthesising a polymer, the method comprising:

-   -   (i) polymerising one or more 2-substituted-2-oxazoline monomers,        one or more 2-substituted-2-oxazine monomers, or a mixture        thereof in the presence of an initiator;    -   (ii) partially hydrolysing the product formed in step (i); and,    -   (iii) performing a Michael addition reaction to react one or        more acrylate or methacrylate species with the product of step        (ii).

In a preferred embodiment in step (iii), the Michael addition reactionreacts an alk-2-yn-1-yl-acrylate species with the product of step (ii).

In a more preferred embodiment, in a further step (iv), the product ofstep (iii) is reacted with an alkyl azide or a primary alkyl thiol.Preferably, the alk-2-yn-1-yl-acrylate species isprop-2-yn-1-yl-acrylate (propargyl acrylate).

Lubricating Compositions

Lubricating compositions of the invention may be lubricants suitable foruse as motor vehicle motor oils comprising a major amount of oil oflubricating viscosity and minor amounts of performance-enhancingadditives, including the polymeric material. The lubricating compositionmay also be in the form of an additive concentrate for blending with oilof lubricating viscosity to make a final lubricant.

Preferably the lubricating compositions of the invention will contain0.01 to 25 percent by mass, based on the mass of the composition of thepolymer, more preferably 0.01 to 10, for example up to 0.5, 1, 2, 3, 4or 5 percent by mass, based on the mass of the composition. When in theform of an additive concentrate, typically the polymer will be presentin an oil of lubricating viscosity in an amount of 30 to 50 percent bymass, based on the mass of the composition.

The oil of lubricating viscosity (sometimes referred to as “base stock”or “base oil”) is the primary liquid constituent of a lubricant, intowhich additives and possibly other oils are blended, for example toproduce a final lubricant (or lubricant composition). A base oil, whichis useful for making additive concentrates as well as for makinglubricating oil compositions therefrom, may be selected from naturaloils (vegetable, animal or mineral) and synthetic lubricating oils andmixtures thereof.

Definitions for the base stocks and base oils in this invention are thesame as those found in the American Petroleum Institute (API)publication “Engine Oil Licensing and Certification System”, IndustryServices Department, Fourteenth Edition, December 1996, Addendum 1,December 1998, which categorizes base stocks as follows:

-   -   a) Group I base stocks contain less than 90 percent saturates        and/or greater than 0.03 percent sulphur and have a viscosity        index greater than or equal to 80 and less than 120 using the        test methods specified in Table E-1.    -   b) Group II base stocks contain greater than or equal to 90        percent saturates and less than or equal to 0.03 percent sulphur        and have a viscosity index greater than or equal to 80 and less        than 120 using the test methods specified in Table E-1.    -   c) Group III base stocks contain greater than or equal to 90        percent saturates and less than or equal to 0.03 percent sulphur        and have a viscosity index greater than or equal to 120 using        the test methods specified in Table E-1.    -   d) Group IV base stocks are polyalphaolefins (PAO).    -   e) Group V base stocks include all other base stocks not        included in Group I, II, III, or IV.

Typically, the base stock has a viscosity preferably of 3-12, morepreferably 4-10, most preferably 4.5-8, mm²/s at 100° C.

TABLE E-1 Analytical Methods for Base Stock Property Test MethodSaturates ASTM D 2007 Viscosity Index ASTM D 2270 Sulphur ASTM D 2622ASTM D 4294 ASTM D 4927 ASTM D 3120

Preferably, the oil of lubricating viscosity comprises greater than orequal to 10, more preferably greater than or equal to 20, even morepreferably greater than or equal to 25, even more preferably greaterthan or equal to 30, even more preferably greater than or equal to 40,even more preferably greater than or equal to 45, mass % of a Group IIor Group III base stock, based on the total mass of the oil oflubricating viscosity. Even more preferably, the oil of lubricatingviscosity comprises greater than 50, preferably greater than or equal to60, more preferably greater than or equal to 70, even more preferablygreater than or equal to 80, even more preferably greater than or equalto 90, mass % of a Group II or Group III base stock, based on the totalmass of the oil of lubricating viscosity. Most preferably, the oil oflubricating viscosity consists essentially of a Group II and/or GroupIII base stock. In some embodiments the oil of lubricating viscosityconsists solely of Group II and/or Group III base stock. In the lattercase it is acknowledged that additives included in the lubricating oilcomposition may comprise a carrier oil which is not a Group II or GroupIII base stock.

Other oils of lubricating viscosity that may be included in thelubricating oil composition are detailed as follows:

Natural oils include animal and vegetable oils (e.g. castor and lardoil), liquid petroleum oils and hydro refined, solvent-treated minerallubricating oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale are also useful base oils.

Synthetic lubricating oils include hydrocarbon oils such as polymerizedand interpolymerized olefins (e.g. polybutylenes, polypropylenes,propylene-isobutylene copolymers, chlorinated polybutylenes,poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g.dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes,di(2-ethylhexyl)benzenes); polyphenols (e.g. biphenyls, terphenyls,alkylated polyphenols); and alkylated diphenyl ethers and alkylateddiphenyl sulfides and the derivatives, analogues and homologues thereof.

Another suitable class of synthetic lubricating oil comprises the estersof dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinicacids and alkenyl succinic acids, maleic acid, azelaic acid, subericacid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer,malonic acid, alkylinalonic acids, alkenyl malonic acids) with a varietyof alcohols (e.g. butyl alcohol, hexyl alcohol, dodecyl alcohol,2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether,propylene glycol). Specific examples of these esters include dibutyladipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols, and polyol ethers such as neopentylglycol, trimethyloipropane, pentaerythritol, dipentaerythritol andtripentaerythritol.

Unrefined, refined and re-refined oils can be used in the compositionsof the present invention. Unrefined oils are those obtained directlyfrom a natural or synthetic source without further purificationtreatment. For example, a shale oil obtained directly from retortingoperations, a petroleum oil obtained directly from distillation or esteroil obtained directly from an esterification process and used withoutfurther treatment would be unrefined oil. Refined oils are similar tothe unrefined oils except they have been further treated in one or morepurification steps to improve one or more properties. Many suchpurification techniques, such as distillation, solvent extraction, acidor base extraction, filtration and percolation, are known to thoseskilled in the art. Re-refined oils are obtained by processes similar tothose used to obtain refined oils applied to refined oils that have beenalready used in service. Such re-refined oils are also known asreclaimed or reprocessed oils and often are additionally processed bytechniques for treating spent additive and oil breakdown products.

Other examples of base oil are gas-to-liquid (“GTL”) base oils, i.e. thebase oil may be an oil derived from Fischer-Tropsch synthesisedhydrocarbons made from synthesis gas containing H₂ and CO using aFischer-Tropsch catalyst. These hydrocarbons typically require furtherprocessing in order to be useful as a base oil. For example, they may,by methods known in the art, be hydroisomerized; hydrocracked andhydroisomerized; dewaxed; or hydroisomerized and dewaxed.

The oil of lubricating viscosity may also comprise a Group I, Group IVor Group V base stocks or base oil blends of the aforementioned basestocks.

The lubricating compositions of the present invention preferablycomprise at least 60% by weight, for example 70% by weight or more of anoil of lubricating viscosity, based on the weight of the composition.

Co-Additives

The lubricating oil compositions of all aspects of the present inventionmay further comprise one or more phosphorus-containing compounds;oxidation inhibitors or anti-oxidants; dispersants; metal detergents;and other co-additives, provided they are different from the polymercomprising units (a) and one or both units (b) and (c). These will bediscussed in more detail below.

Suitable phosphorus-containing compounds include dihydrocarbyldithiophosphate metal salts, which are frequently used as antiwear andantioxidant agents. The metal is preferably zinc, but may be an alkalior alkaline earth metal, or aluminium, lead, tin, molybdenum, manganese,nickel or copper. The zinc salts are most commonly used in lubricatingoil in amounts of 0.1 to 10, preferably 0.2 to 2 mass %, based upon thetotal weight of the lubricating oil composition. They may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂S₅, and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared where the hydrocarbyl groups onone are entirely secondary in character and the hydrocarbyl groups onthe others are entirely primary in character. To make the zinc salt, anybasic or neutral zinc compound could be used but the oxides, hydroxidesand carbonates are most generally employed. Commercial additivesfrequently contain an excess of zinc due to the use of an excess of thebasic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil-soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula:

wherein R and R′ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethyihexyl, phenyl, butylphenyl, cyclohexyl, methyleyclopentyl,propenyl, butenyl. In order to obtain oil solubility, the total numberof carbon atoms (i.e. R and R′) in the dithiophosphoric acid willgenerally be 5 or greater. The zinc dihydrocarbyl dithiophosphate (ZDDP)can therefore comprise zinc dialkyl dithiophosphates. Lubricating oilcompositions of the present invention suitably may have a phosphoruscontent of no greater than about 0.08 mass % (800 ppm). Preferably, inthe practice of the present invention, ZDDP is used in an amount closeor equal to the maximum amount allowed, preferably in an amount thatprovides a phosphorus content within 100 ppm of the maximum allowableamount of phosphorus. Thus, lubricating oil compositions useful in thepractice of the present invention preferably contain ZDDP or otherzinc-phosphorus compounds, in an amount introducing from 0.01 to 0.08mass % of phosphorus, such as from 0.04 to 0.08 mass % of phosphorus,preferably, from 0.05 to 0.08 mass % of phosphorus, based on the totalmass of the lubricating oil composition.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service. Oxidative deterioration can be evidenced bysludge in the lubricant, varnish-like deposits on the metal surfaces,and by viscosity growth. Such oxidation inhibitors include hinderedphenols, alkaline earth metal salts of alkylphenolthioesters havingpreferably C₅ to C₁₂ alkyl side chains, calcium nonylphenol sulfide, oilsoluble phenates and sulfurized phenates, phosphosulfurized orsulfurized hydrocarbons or esters, phosphorous esters, metalthiocarbamates, oil soluble copper compounds as described in U.S. Pat.No. 4,867,890, and is molybdenum-containing compounds.

Aromatic amines having at least two aromatic groups attached directly tothe nitrogen constitute another class of compounds that is frequentlyused for antioxidancy. Typical oil-soluble aromatic amines having atleast two aromatic groups attached directly to one amine nitrogencontain from 6 to 16 carbon atoms. The amines may contain more than twoaromatic groups. Compounds having a total of at least three aromaticgroups in which two aromatic groups are linked by a covalent bond or byan atom or group (e.g., an oxygen or sulfur atom, or a —CO—, —SO₂— oralkylene group) and two are directly attached to one amine nitrogen arealso considered aromatic amines having at least two aromatic groupsattached directly to the nitrogen. The aromatic rings are typicallysubstituted by one or more substituents selected from alkyl, cycloalkyl,alkoxy, aryloxy, acyl, acylamino, hydroxy, and nitro groups. The amountof any such oil soluble aromatic amines having at least two aromaticgroups attached directly to one amine nitrogen should preferably notexceed 0.4 mass %.

A dispersant is an additive whose primary function is to hold solid andliquid contaminations in suspension, thereby passivating them andreducing engine deposits at the same time as reducing sludgedepositions. For example, a dispersant maintains in suspensionoil-insoluble substances that result from oxidation during use of thelubricant, thus preventing sludge flocculation and precipitation ordeposition on metal parts of the engine.

Dispersants in this invention are preferably “ashless”, as mentionedabove, being non-metallic organic materials that form substantially noash on combustion, in contrast to metal-containing and hence ash-formingmaterials, They comprise a long hydrocarbon chain with a polar head, thepolarity being derived from inclusion of e.g. an O, P, or N atom, Thehydrocarbon is an oleophilic group that confers oil-solubility, having,for example 40 to 500 carbon atoms. Thus, ashless dispersants maycomprise an oil-soluble polymeric backbone.

A preferred class of olefin polymers is constituted by polybutenes,specifically polyisobutenes (PIS) or poly-n-butenes, such as may beprepared by polymerization of a C₄ refinery stream.

Dispersants include, for example, derivatives of long chainhydrocarbon-substituted carboxylic acids, examples being derivatives ofhigh molecular weight hydrocarbyl-substituted succinic acid. Anoteworthy group of dispersants is constituted byhydrocarbon-substituted succinimides, made, for example, by reacting theabove acids (or derivatives) with a nitrogen-containing compound,advantageously a polyalkylene polyamine, such as a polyethylenepolyamine. Particularly preferred are the reaction products ofpolyalkylene polyamines with alkenyl succinic anhydrides, such asdescribed in U.S. Pat. Nos 3,202,678; 3,154,560; 3,172,892; 3,024,195;3,024,237, 3,219,666; and 3,216,936, that may be post-treated to improvetheir properties, such as borated (as described in U.S. Pat. Nos.3,087,936 and 3,254,025), fluorinated or oxylated. For example, borationmay be accomplished by treating an acyl nitrogen-containing dispersantwith a boron compound selected from boron oxide, boron halides, boronacids and esters of boron acids.

Preferably, the dispersant, if present, is a succinimide-dispersantderived from a polyisobutene of number average molecular weight in therange of 1000 to 3000, preferably 1500 to 2500, and of moderatefunctionality. The succinimide is preferably derived from highlyreactive polyisobutene.

Another example of dispersant type that may be used is a linked aromaticcompound such as described in EP-A-2 090 642.

A detergent is an additive that reduces formation of piston deposits,for example high-temperature varnish and lacquer deposits in engines; itnormally has acid-neutralising properties and is capable of keepingfinely-divided solids in suspension. Most detergents are based on metal“soaps”, that is metal salts of acidic organic compounds.

Detergents generally comprise a polar head with a long hydrophobic tail,the polar head comprising the metal salt of the acidic organic compound.The salts may contain a substantially stoichiometric amount of the metalwhen they are usually described as normal or neutral salts and wouldtypically have a total base number or TBN at 100% active mass (as may bemeasured by ASTM D2896) of from 0 to 80. Large amounts of a metal basecan be included by reaction of an excess of a metal compound, such as anoxide or hydroxide, with an acidic gas such as carbon dioxide.

The resulting overbased detergent comprises neutralised detergent as anouter layer of a metal base (e.g. carbonate) micelle. Such overbaseddetergents may have a TBN at 100% active mass of 150 or greater, andtypically of from 200 to 500 or more.

Suitably, detergents that may be used include oil-soluble neutral andoverbased sulfonates, phenates, sulfurised phenates, thiophosphonates,salicylates and naphthenates and other oil-soluble carboxylates of ametal, particularly alkali metal or alkaline earth metals, e.g. Na, K,Li, Ca and Mg. The most commonly-used metals are Ca and Mg, which mayboth be present in detergents used in lubricating compositions, andmixtures of Ca and/or Mg with Na. Detergents may be used in variouscombinations.

Additional additives may be incorporated into the compositions of theinvention to enable particular performance requirements to be met.Examples of such additives which may be included in the lubricating oilcompositions of the present invention are metal rust inhibitors,viscosity index improvers, corrosion inhibitors, oxidation inhibitors,other friction modifiers, anti-foaming agents, anti-wear agents and pourpoint depressants. Some are discussed in further detail below.

Friction modifiers and fuel economy agents that are compatible with theother ingredients of the final oil may also be included. Examples ofsuch materials include glyceryl monoesters of higher fatty acids, forexample, glyceryl mono-oleate; esters of long chain polycarboxylic acidswith diols, for example, the butane diol ester of a dimerizedunsaturated fatty acid; and alkoxylated alkyl-substituted mono-amines,diamines and alkyl ether amines, for example, ethoxylated tallow amineand ethoxylated tallow ether amine.

Other known friction modifiers comprise oil-soluble organo-molybdenumcompounds. Such organo-molybdenum friction modifiers also provideantioxidant and antiwear credits to a lubricating oil composition.Examples of such oil-soluble organo-molybdenum compounds includedithiocarbamates, dithiophosphates, dithiophosphinates, xanthates,thioxanthates, sulfides, and the like, and mixtures thereof.Particularly preferred ate molybdenum dithiocarbamates,dialkyldithiophosphates, alkyl xanthates and alkylthioxanthates.

Additionally, the molybdenum compound may be an acidic molybdenumcompound. These compounds will react with a basic nitrogen compound asmeasured by ASTM test D-664 or D-2896 titration procedure and aretypically hexavalent. Included are molybdic acid, ammonium molybdate,sodium molybdate, potassium molybdate, and other alkali metal molybdatesand other molybdenum salts, e.g., hydrogen sodium molybdate, MoOCl₄,MoO₂Br₂, Mo₂O₃Cl₆, molybdenum trioxide or similar acidic molybdenumcompounds.

Among the molybdenum compounds useful in the compositions of thisinvention are organo-molybdenum compounds of the formula

Mo(R″OCS₂)₄ and

Mo(R″SCS₂)₄

wherein R″ is an organo group selected from the group consisting ofalkyl, aryl, aralkyl and alkoxyalkyl, generally of from 1 to 30 carbonatoms, and preferably 2 to 12 carbon atoms and most preferably alkyl of2 to 12 carbon atoms. Especially preferred are thedialkyldithiocarbamates of molybdenum.

Another group of organo-molybdenum compounds useful in the lubricatingcompositions of this invention are trinuclear molybdenum compounds,especially those of the formula Mo₃S_(k)L_(n)Q_(z) and mixtures thereofwherein the L are independently selected ligands having organo groupswith a sufficient number of carbon atoms to render the compound solubleor dispersible in the oil, n is from 1 to 4, k varies from 4 to 7, Q isselected from the group of neutral electron donating compounds such aswater, amines, alcohols, phosphines, and ethers, and z ranges from 0 to5 and includes non-stoichiometric values. At least 21 carbon atomsshould be present among all the ligand organo groups, such as at least25, at least 30, or at least 35, carbon atoms.

Lubricating oil compositions useful in all aspects of the presentinvention preferably contain at least 10 ppm, at least 30 ppm, at least40 ppm and more preferably at least 50 ppm molybdenum. Suitably,lubricating oil compositions useful in all aspects of the presentinvention contain no more than 1000 ppm, no more than 750 ppm or no morethan 500 ppm of molybdenum. Lubricating oil compositions useful in allaspects of the present invention preferably contain from 10 to 1000,such as 30 to 750 or 40 to 500, ppm of molybdenum (measured as atoms ofmolybdenum).

The viscosity index of the base stock is increased, or improved, byincorporating therein certain polymeric materials that function asviscosity modifiers (VM) or viscosity index improvers (VII). Generally,polymeric materials useful as viscosity modifiers are those havingnumber average molecular weights (Mn) of from 5,000 to 250,000,preferably from 15,000 to 200,000, more preferably from 20,000 to150,000. These viscosity modifiers can be grafted with graftingmaterials such as, for example, maleic anhydride, and the graftedmaterial can be reacted with, for example, amines, amides,nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional viscosity modifiers (dispersant-viscosity modifiers).

Polymers prepared with diolefins will contain ethylenic unsaturation,and such polymers are preferably hydrogenated. When the polymer ishydrogenated, the hydrogenation may be accomplished using any of thetechniques known in the prior art. For example, the hydrogenation may beaccomplished such that both ethylenic and aromatic unsaturation isconverted (saturated) using methods such as those taught, for example,in U.S. Pat. Nos. 3,113,986 and 3,700,633 or the hydrogenation may beaccomplished selectively such that a significant portion of theethylenic unsaturation is converted while little or no aromaticunsaturation is converted as taught, for example, in U.S. Pat. Nos.3,634,595; 3,670,054; 3,700,633 and Re 27,145. Any of these methods canalso be used to hydrogenate polymers containing only ethylenicunsaturation and which are free of aromatic unsaturation.

Pour point depressants (PPD), otherwise known as lube oil flow improvers(LOFIs) lower the lowest temperature at which the lube flows. Comparedto VM, LOFIs generally have a lower number average molecular weight.Like VM, LOFIs can be grafted with grafting materials such as, forexample, maleic anhydride, and the grafted material can be reacted with,for example, amines, amides, nitrogen-containing heterocyclic compoundsor alcohol, to form multifunctional additives.

In the present invention it may be necessary to include an additivewhich maintains the stability of the viscosity of the blend. Thus,although polar group-containing additives achieve a suitably lowviscosity in the pre-blending stage, it has been observed that somecompositions increase in viscosity when stored for prolonged periods.Additives which are effective in controlling this viscosity increaseinclude the long chain hydrocarbons functionalized by reaction withmono- or dicarboxylic acids or anhydrides which are used in thepreparation of the ashless dispersants as hereinbefore disclosed.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount that enables the additive to provide its desired function.Representative effective amounts of such additives, when used incrankcase lubricants, are listed below. All the values listed (with theexception of detergent values since the detergents are used in the formof colloidal dispersants in an oil) are stated as mass percent activeingredient (A.I.).

MASS % MASS % ADDITIVE (Broad) (Preferred) Dispersant 0.1-20   1-8 MetalDetergents 0.1-15  0.2-9  Corrosion Inhibitor 0-5   0-1.5 Metaldihydrocarbyl dithiophosphate 0.1-6  0.1-4  Antioxidant 0-5 0.01-2.5Pour Point Depressant 0.01-5   0.01-1.5 Antifoaming Agent 0-5 0.001-0.15Supplemental Antiwear Agents  0-1.0   0-0.5 Friction Modifier 0-5  0-1.5 Viscosity Modifier 0.01-10  0.25-3  Base stock Balance Balance

Preferably, the Noack volatility of the fully formulated lubricating oilcomposition (oil of lubricating viscosity plus all additives) is nogreater than 18, such as no greater than 14, preferably no greater than10, mass %. Lubricating oil compositions useful in the practice of thepresent invention may have an overall sulfated ash content of from 0.5to 2.0, such as from 0.7 to 1.4, preferably from 0.6 to 1.2, mass %.

It may be desirable, although not essential, to prepare one or moreadditive concentrates comprising additives (concentrates sometimes beingreferred to as additive packages) whereby several additives can be addedsimultaneously to the oil to form the lubricating oil composition.

EXAMPLES

The invention will now be particularly described in the followingnon-limiting examples.

Synthesis of Polymers

In a first step, a 2-substituted-2-oxazoline polymer is formed, Thesynthesis was as set out, for example, in EP 3 257 921 A1. A2-substituted 2-oxazoline monomer, where the substituent was derivedfrom a fatty acid containing a mixture of singly, doubly andtriply-unsaturated Cr alkenyl groups (from rape-seed oil), was chargedto a reaction flask and methyl tosylate was added in a monomer toinitiator ratio of 50:1. This reaction mixture was stirred at 140° C.for 1 hour 10 minutes. The polymer had a number average molecular weight(Mn) of 10500 g/mol and a dispersity (Ð) of 1.36 as measured using GPCwith narrow PMMA standards. The structure of the polymer was as follows:

In a second step, the polymer obtained in the first step was partiallyhydrolysed by treating with a 2:8 ( )N) mixture of 35% HCl(aq) and THFfor 1 hour at 120° C. in a sealed vial in a microwave synthesiser. Theresulting solution was precipitated in acetone, Then, the mixture wasdissolved in THF and 4M NaOH was added until the pH was <9. The THF wasremoved in vacua, and the resulting precipitate filtered and washed withwater. This produced a partially hydrolysed polymer having thestructure:

In a third step, the polymer obtained in the second step was sealed intoa vial with a THF solution of propargyl acrylate (3 eq) andtrimethylamine (3 eq). The vial was placed into a microwave synthesiserand heated to 130° C. for 3 hours. The product was twice precipitated inslightly acidic methanol to remove the excess trimethylamine andpropargyl acrylate. This promoted a Michael addition reaction to yield apolymer having the structure:

Two alternative fourth steps were then performed on the polymer obtainedfrom the third step.

In one synthesis, the polymer was subjected to an azide alkyne “click”reaction by reacting it with hexadecyl azide in the presence of Cu(0)wire in THF at 50° C. overnight. The resultant polymer had thestructure:

In another synthesis, the polymer from the third step was subjected to athiol. yne “click” reaction by reacting it, in a sealed, degassed vialwith dodecanethiol (2 eqs) in the presence of AIBN (25 mol %) in THF at75° C. overnight. The resultant polymer had the structure:

Tests and Results

Two Example oils were prepared (amounts are expressed as weightproportions)

Reference Example 1 Example 2 Gp I base oil 100 99 99 Structure (II)where 1 R3 is 2-ethylhexyl Structure (II) where 1 R3 is hexadecyl

Solubility

Examples 1 and 2 remained clear and bright and homogeneous for over fourmonths after blending.

Viscosity

High Temperature High Shear (HTHS) viscosity measurements conducted at150° C. demonstrate the very low viscomettic contribution of theexamples of the invention compared to a Reference oil:

Reference Example 1 Example 2 HTHS150 (cPs) 1.80 1.84 1.81

Interfacial Tension

Measurements of interfacial tension were carried out on a Krüss DSA100using the pendant drop method.

Both Examples provide significant reduction in interfacial tensionrelative to the Reference. This is indicative of surface activity whichis desirable for wear protection.

Reference Example 1 Example 2 Equilibrated oil-in-water 33.3 10.04 10.69interfacial tension

Friction

Friction coefficients were measured on a PCS Instruments Mini TractionMachine (MTM) fitted with AISI 52100 steel substrates.

Both Examples demonstrate a reduction in friction over the base oil,which is indicative of surface activity and is desirable for fueleconomy.

Reference Example 1 Example 2 Friction coefficient measured at 0.08930.0771 0.0812 135° C. and 20 mm/s rolling speed

What is claimed is:
 1. A lubricating oil composition comprising at least50 percent by mass, based on the mass of the composition, of an oil oflubricating viscosity and 0.01 to 25 percent by mass, based on the massof the composition, of a polymer comprising units (a) and one or bothunits (b) and (c):—N(COR¹)(CH₂)_(x)—  (a)—NH(CH₂)_(y)—  (b)—N(CH₂CH_(2-k)(CH₃)_(k)COOR²)(CH₂)_(z)   (c) wherein the total number(n) of units (a), (b) and (c) is an integer between 4 and 500; whereinx, y and z are independently 2 or 3; wherein k is zero or 1; wherein thepolymer carries an inorganic or organic nucleophilic polymerisationterminating group (t), and an initiator group (i) connected to the Natom of a unit (a), (b) or (c), the initiator group (i) being effectiveto initiate the polymerisation of linear, branched or cyclic hydrocarbylmoieties; wherein R¹ comprises a single or a mixture of linear, branchedor cyclic hydrocarbyl groups having 1-50 carbon atoms, some or allhaving 12-50 carbon atoms, or of at least one macro-monomerichydrocarbyl group with more than 50 carbon atoms; and wherein R²comprises a substituted or unsubstituted hydrocarbyl group having 1 to30 carbon atoms, which group may be, linear or branched or cyclic,saturated or unsaturated, or aromatic.
 2. A lubricating oil compositionaccording to claim 1, wherein R¹ contains 1 to 36 carbon atoms, providedthat some or all of the groups R¹ have 12 to 36 carbon atoms.
 3. Alubricating oil composition according to claim 1, wherein at least 5% ofthe total number of the groups R¹ in the polymer comprise unsaturatedhydrocarbyl groups having between 8 and 20 carbon atoms.
 4. Alubricating oil composition according to claim 3, wherein at least 5% ofthe total number of the groups R¹ in the polymer comprise unsaturatedhydrocarbyl groups having between 15 and 20 carbon atoms.
 5. Alubricating oil composition according to claim 1, wherein groups R¹ aobtained from natural fatty acids.
 6. A lubricating oil compositionaccording to claim 5, wherein groups R¹ are obtained from tall oil fattyacid and/or rape-seed oil fatty acid.
 7. A lubricating oil compositionaccording to claim 1, wherein R² is a group (CH₂)_(m)CCH, where m is aninteger from 1 to 10; a hydrocarbyl group terminally substituted by a1,2,3-triazole group; or a hydrocarbyl group terminally substituted byone or more thioether groups.
 8. A lubricating oil composition accordingto claim 1, wherein the polymer does not comprise any units (c).
 9. Alubricating oil composition according to claim 1, wherein the polymerdoes not comprise any units (b).
 10. A lubricating oil compositionaccording to claim 1, wherein n is from 10 to
 300. 11. A lubricating oilcomposition according to claim 10, wherein n is from 25 to
 100. 12. Alubricating oil composition according to claim 1, comprising one or moreco-additives different from the polymer comprising units (a) and one orboth units (b) and (c), the one or more co-additives being selected fromone or more phosphorus-containing compounds; oxidation inhibitors orantioxidants; dispersants; metal-containing detergents; anti-wearagents; friction modifiers; and viscosity modifiers.
 13. A lubricatingoil composition according to claim 1, comprising at least 70% by mass ormore of an oil of lubricating viscosity, based on the mass of thecomposition,
 14. A method of lubricating the crankcase of an internalcombustion engine comprising operating the engine and lubricating thecrankcase with a lubricating oil composition according to claim
 1. 15. Amethod for synthesising a polymer, said method comprising: (i)polymerising one or more 2-substituted-2-oxazoline monomers, one or more2-substituted-2-oxazine monomers, or a mixture thereof in the presenceof an initiator; (ii) partially hydrolysing the product formed in step(i); and, (iii) performing a Michael addition reaction to react one ormore acrylate or methacrylate species with the product of step (ii). 16.The method of claim 13, wherein in step (iii), the Michael additionreaction reacts an alk-2-yn-1-yl-acrylate species with the product ofstep (ii).
 17. The method of claim 16, further comprising a step (iv),where the product of step (iii) is reacted with an alkyl azide or aprimary alkyl thiol.